I'm not sure if this applied to all artists during the 30's/40's/50's but I do know that quite a few creators saw comics as merely a stepping stone to getting work in the big times - newspapers.  

I don't know that I would necessarily use the word "better" as that's a bit vague.  But I would argue that modern comic book artists have to work to a different set of standards that didn't exist in the earlier days.  Today's artists usually can't do more than one book a month, and even then they sometimes need a fill-in or have trouble making deadlines.  I would say a lot of that has to do with modern readers expecting more detail out of the artwork.  In prior eras, you could get away with having no backgrounds or minimal backgrounds, just figure work with people fighting, etc.  Interior pages were mostly panel pages, not big double page spreads or splash pages.  I remember the first time I looked at Jack Kirby's work on early issues of the Avengers, and was surprised at how simple the art was.  That's not to say that it wasn't good or that it didn't reflect talent or skill -- it's just indicative of how comics were different.  Modern comic book readers today expect detailed, highly rendered artwork that is time consuming.  It seems like guys like Art Adams, George Perez, and John Byrne had a big influence on the Image guys, who in turn influenced a lot of the artists we are seeing today that have similarly detailed art styles.  And given the huge popularity the Image guys had, it's no surprise that their fingerprints are all over the look of modern comics.

Now that being said -- I would also argue that another difference compared to the old days, at least within superhero comics, is a greater stylistic diversity.  Sure, there was diversity in the past as well, but I would argue it was diversity within a genre.  Whereas today we're increasingly seeing different genres.  Whatever else you may think of their art, guys like Chris Samnee, Humberto Ramos, Chris Bachalo, Sean Gordon Murphy, Michael Lark, David Finch, Francis Manapul, and David Aja have wildly different styles.  And with the success of Image and other non-big-two publishers, I think modern audiences are coming around to, and expecting, more artists to depart from the "traditional superhero comic art" look.

As others said, a huge part of this question deals with the expectation of today's readers, the expectation of 'how many lines used for rendering on every figure in every panel'.

every line takes time. A 1987 Steve Rude page takes 1/3rd the physical labour (and therefore, time) than is demanded by a Finch page.

Totally agree. "Detail" has been a red herring in comic art for a long time, but especially since the late silver age. I've seen plenty of art with a lot of little lines and excess rendering that gives no thought to composition, anatomy, or storytelling.

"I try to get it simpler and simpler as time goes on... The rest is embroidery. When I'm in a rush, I use a lot of detail, but when I have time I try to keep it simple, and that takes time because you know it's eliminating and eliminating and eliminating and get it down to its essence." --Al Hirschfeld

George Perez has Been  a legend for the last 30 years but the only time I really liked his "detail" was in the Avengers/ JLA crossover. Pretty much all other times, it was a distraction. How many bricks does he have to draw in the wall ?

I'll admit to liking Perez when inked by the likes of Jack Abel, who reduced the amount of detail. I loved his work in the 70s and 80s, but was getting jaded with it in the 90s to the point where the run with Busiek really started to grate with me. It felt like it was more and more of the same, faces, poses etc, but to be fair when you have a body of work like he does you've probably drawn the same scene a few times.
Is it the modern audience, or editor that wants the superdetail, because if you look at some of the breakout talent lately there are quite a few doing great work with simpler styles. Samnee, Staples, David Lopez, Allred(sorry loatheswareluvskane) , Dillon(I'm well aware he aint new), and Francavilla come to mind.